Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system. MS attacks occur less frequently during pregnancy, which is likely due to the increased production of steroidal sex hormones. Similarly, the severity of experimental autoimmune encephalomyelitis (EAE), an MS-like disease in mice, is also diminished during pregnancy. In mice, steroidal estrogens can inhibit anti-myelin helper T-lymphocyte responses and suppress EAE. In some women with MS, steroidal estrogens can decrease the number of demyelinating lesions in the CNS. Nevertheless, steroidal estrogens have a limited therapeutic potential because their long-term use increases the risk for hormone-related cancers. Consequently, the development of non-steroidal estrogens that reduce the severity of MS, while minimizing risks, is highly desirable. One class of non-steroidal estrogens that may have the capacity to suppress MS is phytoestrogens. Phytoestrogens are plant-derived compounds that are structurally similar to steroidal estrogens. Unlike steroidal estrogens, however, they have a higher affinity for estrogen receptor-beta (ER-beta) than for estrogen receptor-alpha (ER-alpha). Because of the distinct tissue distribution of these two receptors, phytoestrogens have potent estrogen-agonist activity in bone and cardiovascular tissues, yet lack activity in breast and uterine tissues. In addition, phytoestrogens may regulate immune cell function, based on our recent discovery that ER-beta is expressed by immune cells. The therapeutic potential of phytoestrogens in MS, has yet to be studied. Isoflavones derived from soybeans are a rich source of phytoestrogens. Genistein, daidzein, and glycitein are the major isoflavones derived from soy. Our preliminary experiments found that the severity of EAE was diminished in mice treated either with a soy isoflavone preparation or genistein, and that this suppression occurred in the absence of injury to the reproductive system. In addition, soy isoflavone-treated mice had a reduced capacity to respond to myelin antigens and to produce TNF-alpha, a cytokine that is essential to the pathogenesis of EAE and MS. These data support our hypotheses that soy isoflavones reduce the severity of EAE by an ER-beta dependent pathway, which diminishes the capability of helper T lymphocytes to proliferate and secrete TNF-alpha, and results in the suppression of inflammation and demyelination in the CNS. The main objectives of this proposal are: (1) To identify the soy-isoflavones with the greatest ability to suppress EAE, (2) To determine whether soy isoflavone-mediated inhibition of TNF-alpha and suppression of EAE are dependent on signaling through ER-beta, (3) To determine which immune cells express ER-beta and whether transcription of immunologically relevant genes is regulated by soy isoflavones. [unreadable] [unreadable]